Sienna Caldwell stands at about 4'11 and has an athletic, slim build. She has golden blonde hair that goes about 2 inches below her shoulders. She has blue eyes and has light skin with warm undertones.

Sienna is a very sweet girl, but she is competitive, driven by success and she is a high achiever. She can sometimes get jealous, and can sometimes be vengeful, but overall she is a great friend and teammate.

Sienna's parents, Vasilia Vane-Caldwell and Oliver Caldwell are famous in the wizarding world. Her mother, Vasilia, is a shop owner, with a talent for haute couture. Her father, Oliver, is a famous retired professional quidditch player. Sienna's parents have shaped her in many ways, making her competitive, driven, and have given her a taste for fine things. Sienna's mother has guided her to be refined and poised, while her father has taught her how to fly through the air on his broomstick.

The first time Sienna used magic was inside her mother's shop at age 9, where she could usually be found if she wasn't on the quidditch pitch. Her mother asked her to retrieve a roll of silk fabric from the back of the shop, and Sienna willed the roll right into her hand. Because she is a pureblood from the wizarding world it wasn't at all surprising, but it was a very exciting moment for her.